Co-sintered multi-system tungsten alloy composite

ABSTRACT

A composite is produced by the steps of (a) blending a first mixture of metallic powders; (b) compacting the blended first mixture of metallic powders to a plurality of discretely shaped articles; (c) blending a second mixture of metallic powders; (d) mixing the plurality of discretely shaped articles with the blended second mixture of metallic powders to form a precursor blend; (e) compacting the precursor blend; and (f) sintering the precursor blend. The composite has a metallic matrix with embedded shapes dispersed throughout the matrix where the embedded shapes have an incipient liquid phase sintering temperature less than an incipient liquid phase sintering temperature of the matrix.

CROSS REFERENCE TO RELATED APPLICATION(S)

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 60/815,730, titled “Co-Sintered Multi-SystemTungsten Alloy Composite,” that was filed on Jun. 20, 2006. The subjectmatter of that provisional patent application is incorporated byreference in its entirety herein.

U.S. GOVERNMENT RIGHTS

N.A.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a composite material and a method for themanufacture of that composite material. The composite material hasdiscrete liquid phase sintered tungsten heavy alloy shapes embedded in asolid state sintered matrix. Both the liquid phase sintering of theembedded shapes and the solid state sintering of the matrix areperformed at the same temperature using a single co-sintering process.The co-sintering process allows for uniform sintering shrinkage of theembedded shapes and the surrounding matrix and thereby avoids theformation of defects such as pores and cracking that can occur byconventional processes. In one embodiment, the composite is formed intoa component for a fragmentation device having sufficient strength andgenerating sufficient momentum to penetrate fortified defenses prior todetonation. On detonation, the component releases discrete, high densityfragments.

2. Description of the Related Art

The military has a need for devices that can be deployed from a safedistance and distribute a lethal cloud of fast-moving fragments ondetonation. Such devices presently use an embossed steel shell thatbreaks apart along a pattern of thin sections on detonation. Due to therelatively low density of steel, this configuration is not effective forpenetrating defensive fortifications, such as concrete or steel linedbunkers, prior to detonation.

Momentum is a function of (mass) x (velocity). Accordingly, shapedcharge liners and fragmentation devices are frequently formed from atungsten-base alloy. Commonly owned U.S. Patent Application PublicationNo. US2005/0241522A1 titled “Single Phase Tungsten Alloy for ShapedCharge Liner,” published Nov. 3, 2005, discloses a cast metal alloy forforming a shaped charge liner, fragmentation warhead, warhead casing andthe like that is an alloy of cobalt, tungsten and nickel. U.S. Pat. No.6,960,319 titled “Tungsten Alloys for Penetrator Application and Methodof Making Same” discloses a kinetic energy penetrator formed from analloy of tungsten, one or more elements selected from the groupconsisting of nickel, iron, chromium and cobalt and one or more elementsselected from the group consisting of titanium and aluminum. The kineticenergy penetrator is formed by blending a mixture of the powderedelemental components or alloys and then consolidating by solid statesintering. U.S. Pat. No. 6,827,756 titled “Tungsten Heavy Alloy forPenetrating Splinter Shell and Forming Method Thereof” discloses atungsten-molybdenum-nickel-iron shell formed by compacting elemental oralloy powders of the desired composition to form a green blank and thenliquid phase sintering to consolidate. All three of U.S. PatentApplication Publication No. US2005/0241522A1 and U.S. Pat. Nos.6,960,319 and 6,827,756 are incorporated by reference in theirentireties herein.

There remains, therefore, a need for a high density, high strength,component for a fragmentation device that does not have the limitationsof the prior art.

BRIEF SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a composite metalcomponent. This composite has a metallic matrix and embedded shapesdispersed throughout the matrix where the embedded shapes have anincipient liquid phase sintering temperature less than the incipientliquid phase sintering temperature of the matrix.

In one embodiment of the invention, the composite is produced by thesteps of (a) blending a first mixture of metallic powders; (b)compacting the blended first mixture of metallic powders to a pluralityof discretely shaped articles; (c) blending a second mixture of metallicpowders; (d) mixing the plurality of discretely shaped articles with theblended second mixture of metallic powders to form a precursor blend;(e) compacting the precursor blend; and (f) sintering the precursorblend.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in flow chart representation a method for themanufacture of a composite metal component in accordance with theinvention.

FIG. 2 illustrates a nosecone component formed from the composite metalcomponent of the invention.

FIG. 3 illustrates a portion of the nosecone component of FIG. 2 inmagnified cross-sectional view.

FIG. 4 is a photomicrograph illustrating the structure of the compositeof the invention.

FIG. 5 is a photomicrograph illustrating the structure of a compositeformed contrary to the invention.

Like reference numbers and designations in the various drawingsindicated like elements.

DETAILED DESCRIPTION

Throughout this patent application, the following definitions areemployed.

Incipient Liquid Phase Sintering Temperature—the minimum temperatureeffective for liquid phase sintering of a metallic compact.

Liquid phase sintering—sintering of a compact or loose powder aggregateunder conditions where a liquid phase is present during part of thesintering cycle.

Solid state sintering—a sintering procedure for compacts or loose powderaggregates during which no component melts.

Tungsten-base—an alloy or other mixture of metals having a minimum of50%, by weight, of tungsten.

FIG. 1 illustrates in flow chart representation a method for themanufacture of a composite metal component in accordance with theinvention. A first mixture of metallic powders is blended 10 to form asubstantially homogeneous mixture. The powder constituents of this firstpowder mix are selected to have a liquid phase sintering temperatureless than the liquid phase sintering temperature of a second powder mix,but above the solid state sintering temperature of the second powder mixas described hereinbelow. To enhance the momentum of the composite metalcomponent, the first powder mix preferably includes significant amountsof one or more high density metallic constituents. Most preferably, thefirst powder mix is tungsten-base, molybdenum-base, or a mixture oftungsten- and molybdenum-base. Alloys and compounds of these metals,such as ferrotungsten, may also be employed. In addition, one or moreelements that depress the melting temperature of the powder mix arepresent. Such melting point depressors include copper, cobalt, manganeseand combinations of metals with a melting point less than the matrixmaterial.

The blended first powder mix is then compacted 12 into a desired shape.This shape may be spheres, cubes, rectangular blocks or some otherdesired configuration with a diameter or major axis length of at least 2millimeters and typically in the range of 2 mm to 50 mm. Typically, theblended first powder mix will be inserted into a die cavity having thedesired shape and then compacted under a pressure of from about 200 MPato 700 MPa forming a green compact of the desired shape.

A second powder mix is then blended 14 to form a mixture having a liquidphase sintering temperature higher than the liquid phase sinteringtemperature of the first powder mix and a solid state sinteringtemperature less than the liquid phase sintering temperature of thefirst powder. To enhance momentum, the second powder mix is preferablypredominantly formed of high density metals such as tungsten andmolybdenum. Most preferably, the second powder mix is tungsten-base,molybdenum-base or a mixed tungsten- and molybdenum-base. Alloys andcomponents of these metals, such as ferrotungsten, may also be used. Inone embodiment, the second powder mix is a tungsten heavy alloy (WHA)matrix with a composition, by weight, of 10% to 100% tungsten and thebalance nickel, iron, cobalt and/or copper. The first powder mix and thesecond powdered mix are selected such that the incipient liquid phasesintering temperature of the first powder mix is at least 10° C. lessthan the incipient liquid phase sintering temperature of the secondpowder mix and more preferably, the temperature differential is from 20°C. to 50° C. The melting temperature differential is essential asco-sintering of the first powder mix and the second mix without thisdifferential will result in a homogeneous microstructure.

The blended second powder mix 14 and compacted shapes 12 are thencombined 16 to form a substantially homogeneous suspension of compactedshapes 12 in the second powder mix. The ratio of compacted shapes tosecond powder mix can be from about 10% to 70% by weight such that thecompacted shapes form a discontinuous second phase of embedded shapes ina matrix formed of the second powder mix. The combination is thencompacted 18, such as by placing the mix in a die of a desired shape andcompacting under a pressure of from 200 MPa to 700 MPa to form a greencompact. This green compact is then sintered 20 at a temperature whichmeets all three of the following requirements: (a) above the incipientliquid phase sintering temperature of the embedded shapes of the firstpowder; (b) below the incipient liquid phase sintering temperature ofthe second powder mix; and (c) above the incipient solid state sinteringtemperature of the second powder mix. A typical sintering 20 temperatureis between 1200° C. and 1350° C. and preferably between 1225° C. and1275° C.

The sintered composite metal component may be used as is or finished 22by additional forming or machining to form the component of the desiredconfiguration.

The composite metal component is particularly suited for formation intoa nose cone for a fragmenting warhead 24 as shown in cross-sectionalrepresentation FIG. 2. Subsequent to sintering, additional features suchas apertures 26 and threads 28 may be added during the finishing step.

FIG. 3 illustrates in magnified cross-sectional view, a portion of thecomposite metal component formed into the nose cone 24 of FIG. 2. Thecomposite metal component includes a metallic matrix 30 and embeddedshapes 32 dispersed throughout the matrix. Following sintering inaccordance with the invention, the matrix 30 has a microstructurecommensurate with solid state sintering and the embedded shapes 32 havea microstructure commensurate with liquid phase sintering. Anintermetallic rich diffusion layer 34 bonds the matrix and embeddedshapes. On detonation, the matrix fragments release the embedded shapesas high momentum shrapnel. The intermetallic phase also aids in thefracture and separation of the embedded shapes into discrete fragments.

The advantages of the invention will become more apparent from theexamples that follow.

EXAMPLES Example 1

Two grain spheres compacted from, by weight, 95% tungsten-3% nickel-2%copper were embedded in a matrix of, by weight, 72.2% tungsten-19.5%nickel-8.3% iron and sintered at 1250° C. for 5 hours in a hydrogenatmosphere. The resulting microstructure, illustrated at 15× in thephotomicrograph of FIG. 4, shows fully developed liquid phase sinteredspheres surrounded by an intermetallic rich diffusion layer and a solidstate sintered matrix. The density was measured at approximately 14.6grams per cubic centimeter with an elongation of between 1% and 4% andan ultimate tensile strength of between 5 ksi and 20 ksi. The yield wasnot measurable and fracture appeared to occur in the intermetallicregion following the contours of the spheres. It is believed that thebulk properties of the composite can be further improved to approachthose of the matrix phase through the use of secondary heat treatment.

Example 2

The same spheres as used in Example 1 were embedded in a matrix of, byweight, 95.5% tungsten-3.15% nickel-1.35% iron, a conventional tungstenheavy alloy, and then sintered at 1,300° C. for five hours in hydrogen.Both the spheres and the matrix underwent liquid phase sintering and themicrostructure of this sample is illustrated at 15× in FIG. 5. Themicrostructure shows liquid phase sintered spheres in a liquid phasesintered matrix with no apparent intermetallic regions formed. Thedensity was 18.0 grams per cubic centimeter and fracture did not followthe contours of the spheres such that the spheres of this example wouldnot be released on detonation of a fragmenting warhead.

It is apparent that the process and composites of the inventioneliminate the problems of the prior art because both the embedded shapesand the matrix exhibit the same shrinkage but the embedded shapesundergo liquid phase sintering at the sintering temperature while thematrix is limited to solid state sintering such that two discreet phasesremain present. The invention has a reduced amount of materialrequirements and a reduced number of processing steps required to form afinished product.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method for the manufacture of a composite metalcomponent, comprising the steps of: a) blending a first mixture ofmetallic powders; b) compacting said blended first mixture of metallicpowders to a plurality of discretely shaped articles; c) blending asecond mixture of metallic powders; d) mixing said plurality ofdiscretely shaped articles with said blended second mixture of metallicpowders to form a precursor blend; e) compacting said precursor blend;and f) sintering said precursor blend.
 2. The method of claim 1 whereinsaid sintering is at a temperature effective to liquid phase sinter saiddiscretely shaped articles and solid state sinter said second mixture ofpowders.
 3. The method of claim 2 wherein both said first mixture ofpowders and said second mixture of powders are tungsten-base.
 4. Themethod of claim 3 wherein said sintering temperature is between 1200° C.and 1350° C.
 5. The method of claim 4 wherein said sintering temperatureis between 1225° C. and 1275° C.
 6. The method of claim 4 wherein saidfirst mixture of powders is selected to further contain copper and saidsecond mixture of powders is selected to further contain at least one ofiron, nickel and cobalt.
 7. The method of claim 6 including theadditional step of machining said sintered precursor blend to a finishedcomponent.
 8. The method of claim 7 wherein said machining step forms anosecone for a fragmenting warhead.
 9. A method comprising: forming afirst mixture of a first set of metallic powder constituents, the firstmixture having a first incipient liquid phase sintering temperature;forming a second mixture of a second set of metallic powderconstituents, the second mixture having a second incipient liquid phasesintering temperature and an incipient solid phase sinteringtemperature, wherein the first incipient liquid phase sinteringtemperature is less than the second incipient liquid phase sinteringtemperature and greater than the incipient solid phase sinteringtemperature; compacting the first mixture into a plurality of compactedshapes; forming a combination including a suspension of the compactedshapes in the second mixture; compacting the combination; and sinteringthe compacted combination.
 10. A method according to claim 9, whereinthe first mixture includes at least 50% by weight of tungsten,molybdenum or a mixture thereof.
 11. A method according to claim 10,wherein the first mixture further includes a constituent effective todepress the melting point of said first mixture.
 12. A method accordingto claim 11, wherein said constituent includes copper, cobalt, manganeseor a combination thereof.
 13. A method according to claim 9, wherein thesecond mixture includes at least 50% by weight of tungsten, molybdenumor a mixture thereof.
 14. A method according to claim 9, wherein thesecond mixture is a tungsten heavy alloy matrix including 10% to 100% byweight of tungsten, with the balance including nickel, iron, cobaltand/or copper.
 15. A method according to claim 9, wherein the firstincipient liquid phase sintering temperature is at least 10° C. lessthan the second incipient liquid phase sintering temperature.
 16. Amethod according to claim 15, wherein the first incipient liquid phasesintering temperature is from 20° C. to 50° C. less than the secondincipient liquid phase sintering temperature.
 17. A method comprising:mixing a first plurality of metallic powders to form a first mixturehaving a first incipient liquid phase sintering temperature; mixing asecond plurality of metallic powders to form a second mixture having asecond incipient liquid phase sintering temperature and an incipientsolid phase sintering temperature; compacting the first mixture intoshapes of a desired configuration; forming a metallic matrix includingthe second mixture with a plurality of said shapes embedded therein; andsintering the matrix so that the matrix has a microstructurecommensurate with solid state sintering and the embedded shapes have amicrostructure commensurate with liquid state sintering.
 18. A methodaccording to claim 17, wherein the sintering is performed at atemperature above the first incipient liquid phase sinteringtemperature, below the second incipient liquid phase sinteringtemperature, and above the incipient solid phase sintering temperature.19. A method according to claim 17, wherein the first incipient liquidphase sintering temperature is from 20° C. to 50° C. less than thesecond incipient liquid phase sintering temperature.
 20. A methodaccording to claim 17, wherein the sintering is performed so that anintermetallic rich diffusion layer bonds the matrix and the embeddedshapes.